Absolutely 100% a scam looking for fools to buy bitcoin for them. I've seen this email show up a few times in my spam folder. Often it even has your password in the subject line. This is basically because at some point, your email address and password were involved in a data breach. So these guys have your address and your password (at the time of the breach) and are using that knowledge to scare you into paying thousands in bitcoin rather than people see the dirty dirty things you're up to on the internet. This works on many people because, well, lots of people look at porn online.